JP2010023657A - Electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric power steering device including a fail determination means for determining that a control means for controlling drive of a motor for steering assist is abnormal when a target current, which is obtained by correcting, in accordance with a steering condition of a vehicle, a temporary target current derived based on a steering torque applied to a steering member, does not exist in a predetermined determination range, thereby the target current does not exist in the determination range due to the correction, and such a determination that the control means is abnormal can be prevented. <P>SOLUTION: A fail determination range is set by a fail processing unit 50 base on a detected value of a vehicle speed by a vehicle speed sensor 7 so that a size of the fail determination range varies. The fail determination means determines that the control means is abnormal when a motor current value detected by a motor current sensor 60 does not exist in the set fail determination range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electric power steering device that assists steering of a vehicle by driving a motor based on a steering torque applied to a steering shaft by operation of a steering member.

  In steering a vehicle, a rotation operation of a steering wheel as a steering member is transmitted to a steering mechanism via a steering shaft, and the steering wheels (generally, left and right front wheels) are directed by the operation of the steering mechanism. It is implemented by changing. In recent vehicles, an electric power steering device that assists the above steering by adding the power of a steering assist motor to a steering mechanism is widely installed.

  Recently, a target value of a current to be supplied to the motor is obtained based on a steering torque applied to the steering shaft by rotating the steering wheel, and it is determined whether or not the target value exists in a predetermined region, There has been proposed an electric power steering apparatus that outputs a signal indicating an upper limit value of a predetermined area to a motor drive circuit when the target value does not exist in the predetermined area. According to this electric power steering apparatus, it is possible to prevent the motor from being driven based on a target value that is erroneously obtained and the steering assist force from becoming excessive.

  Patent Document 1 discloses an electric power steering apparatus including a main CPU that controls driving of a motor and a sub CPU that determines abnormality of the main CPU. The main CPU obtains a target value of the current to be supplied to the motor based on the steering torque applied to the steering shaft by rotating the steering wheel, and outputs a signal indicating the target value to the motor drive circuit. The sub CPU determines whether or not the target value exists in a predetermined range, and issues a signal to stop the motor to the motor drive circuit when the target value does not exist in the predetermined range. Thereby, it is possible to prevent the motor from being driven based on a target value that is erroneously obtained by an abnormal operation of the main CPU.

Generally, in the electric power steering apparatus, a plurality of maps showing the relationship between the target value and the steering torque are set according to the vehicle speed. Recently, for the purpose of improving the driver's steering feeling, the target value obtained based on the map is corrected according to the steering state such as the steering angle and the steering speed to obtain the corrected target value. There is an electric power steering apparatus in which a motor is driven and controlled based on a target value.
JP 2001-310743 A

  In the electric power steering apparatus that determines whether or not the target value exists in the predetermined region, if the above-described correction is performed, the correction target value may not exist in the predetermined region even though the correct correction target value is obtained. . In this case, not the signal indicating the correction target value but the signal indicating the upper limit value of the predetermined region is output to the motor drive circuit, which causes a problem that the driver's steering feeling deteriorates.

Further, in the electric power steering apparatus having the sub CPU, when the above-described correction is performed, the correction target value does not exist in the predetermined range, and the main CPU is operating normally although the main CPU is operating normally. A signal may be output from the sub CPU to the motor drive circuit. In this case, the motor is stopped and the steering assist force is lost, so that the driver's steering feeling is deteriorated.
The problem that the driver's steering feeling deteriorates is particularly noticeable during low-speed traveling where a large steering assist force is required.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an electric power steering device in which the steering feeling does not deteriorate even when the target value is corrected according to the steering state of the vehicle.

  An electric power steering apparatus according to a first aspect of the present invention includes a steering assist motor, control means for controlling driving of the motor based on a target current determined according to a steering state of the vehicle, and the target current is a predetermined value. An electric power steering apparatus comprising: a determination unit that determines that the control unit is abnormal when the control unit is not present in the range. The range is set so that the range is widened according to the slowness of the traveling speed of the vehicle. A setting means is provided.

  In the electric power steering apparatus according to a second aspect of the invention, the setting means sets the range based on a function that continuously widens and narrows the range according to the slowness of the traveling speed of the vehicle. It is characterized by.

  In the electric power steering apparatus according to a third aspect of the present invention, the control means corrects a temporary target current determined based on a steering torque applied to the steering member according to a steering state of the vehicle, and determines the target current. It is characterized by the above.

  The electric power steering apparatus according to a fourth aspect of the present invention is characterized by comprising means for stopping driving of the motor when the determination means determines that the control means is abnormal.

  The electric power steering apparatus according to a fifth aspect is characterized in that the steering state includes a steering angle or a steering speed.

  According to the electric power steering apparatus of the first aspect of the invention, by changing the predetermined range for abnormality determination, the target current determined according to the steering state of the vehicle deviates from the predetermined range, and the abnormality is erroneously determined. Therefore, it is possible to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to the correction executed when determining the target current. In addition, by changing the predetermined range in accordance with the slowness of the traveling speed of the vehicle, it is possible to prevent a sudden deterioration in steering feeling during low-speed traveling that requires a large steering assist force.

  According to the electric power steering apparatus of the second aspect of the invention, the range is set based on a function that continuously widens and narrows according to the slowness of the vehicle traveling speed, so that the range corresponds to the traveling speed of the vehicle. A predetermined range is set, and the determination means can make an appropriate determination according to the traveling speed of the vehicle.

  According to the electric power steering apparatus of the third invention, the target current is determined by correcting the temporary target current determined based on the steering torque applied to the steering member according to the steering state of the vehicle. It is possible to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to the change in the steering state.

  According to the electric power steering apparatus of the fourth aspect of the invention, when the control means determines that the control means is abnormal, the motor drive is stopped, thereby erroneously obtaining the abnormal operation of the control means. It is possible to prevent the motor from being driven based on the target current thus obtained.

  According to the electric power steering device of the fifth aspect of the invention, it is possible to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to a change in the steering angle or the steering speed.

(Embodiment 1)
Hereinafter, the present invention will be described in detail with reference to the drawings showing an electric power steering apparatus according to Embodiment 1. FIG. 1 is a schematic diagram showing the configuration of the electric power steering apparatus according to the first embodiment.

  The electric power steering apparatus shown in the figure includes a rack shaft 2 that is supported so as to be movable in the axial direction in a rack housing 10 that extends in the left-right direction of the vehicle body, and a pinion housing 20 that crosses the rack housing 10 in the middle. Is provided with a rack and pinion type steering mechanism 1 having a pinion shaft 3 rotatably supported therein.

  Both ends of the rack shaft 2 projecting outward from both sides of the rack housing 10 are connected to knuckle arms 12 and 12 of left and right front wheels 11 and 11 as steering wheels via respective tie rods 13 and 13. The upper end of the pinion shaft 3 protruding from the upper portion of the pinion housing 20 is connected to the lower end of the steering shaft 4 facing the upper position. A pinion (not shown) is formed at the lower part of the pinion shaft 3 extending into the pinion housing 20, and the pinion is formed on the outer surface of the rack shaft 2 at an appropriate length at the intersection with the rack housing 10. Meshed with the rack teeth.

  The steering shaft 4 is rotatably held in a cylindrical column housing 31 and is attached to the interior of a vehicle compartment (not shown) via the column housing 31 while maintaining an inclined posture with the front facing down. Both ends of the steering shaft 4 protrude outward from both the upper and lower sides of the column housing 31, and the downward projecting ends are connected to the pinion shaft 3 as described above. As a steering wheel 30 is fixed.

  With the above configuration, when the steering wheel 30 is rotated left and right, this rotation is transmitted to the pinion shaft 3 via the steering shaft 4, and the rotation of the pinion shaft 3 is racked at the meshing portion between the pinion and the rack teeth. It is converted into movement in the axial length direction of the shaft 2. The movement of the rack shaft 2 thus generated is transmitted to the knuckle arms 12 and 12 of the left and right front wheels 11 and 11 via the tie rods 13 and 13 at both ends, and these knuckle arms 12 and 12 are pushed and pulled to cause the left and right front wheels 11 to move. , 11 is steered.

  The illustrated electric power steering device is based on the torque detection device 5 for detecting the steering torque applied to the steering shaft 4 by the rotation operation of the steering wheel 30 and the detected torque of the torque detection device 5 in the steering operation as described above. And a steering assisting motor 6 driven by the motor.

  The torque detector 5 divides the middle of the steering shaft 4 into two shafts that are coaxially connected via a torsion bar, and detects a relative angular displacement caused by the twist of the torsion bar between these two shafts. Thus, a known configuration for obtaining the steering torque applied to the steering shaft 4 is provided, which is provided inside the column housing 31 as indicated by a broken line in FIG.

  The steering assisting motor 6 is attached to the outside of the column housing 31 below the position where the torque detecting device 5 is disposed, with the shaft core being substantially orthogonal, and rotating the output shaft extending inside the column housing 31. Is transmitted to the steering shaft 4 by being decelerated by a worm gear speed reducer including a worm and a worm wheel, for example, and a rotational force is applied to the steering shaft 4. With this configuration, the rotational force of the steering assisting motor 6 transmitted to the steering shaft 4 at a reduced speed is transmitted to the pinion shaft 3 connected to the lower end of the steering shaft 4, and the rack shaft 2 corresponding to the rotation of the pinion shaft 3. This assists the steering performed as described above.

  The steering assist motor 6 may be attached to the outside of the rack housing 10 or the pinion housing 20 to be transmitted to the rack shaft 2 or the pinion shaft 3. Transmission to the rack shaft 2 can be realized by a configuration in which the rotation of the motor 6 is transmitted to the rack shaft 2 via a motion conversion mechanism such as a ball screw mechanism and a moving force in the axial direction is applied to the rack shaft 2. The transmission to the pinion shaft 3 can be realized in the same manner as the steering shaft 4.

  The electric power steering apparatus includes a control unit 40 that controls the driving of the motor 6 and a fail processing unit 50 that stops the driving of the motor 6 when the control unit 40 is abnormal. The steering assist motor 6 is driven in accordance with a control command given from the control unit 40 via the motor drive circuit 61. The control unit 40 is provided with a detected value of the steering torque by the torque detection device 5 and a detected value of the vehicle speed by the vehicle speed sensor 7 disposed at an appropriate part of the vehicle. Further, the motor 6 for assisting steering is provided with a motor current sensor 60, and the motor current value of the motor 6 detected by the motor current sensor 60 is given to the control unit 40.

  The control unit 40 includes a CPU, a ROM, and a RAM, and executes assist control by the operation of the CPU according to a control program stored in the ROM. In this assist control operation, a temporary target current is obtained according to a control map stored in accordance with the vehicle speed, and the detected value of the steering torque by the torque detection device 5 is determined. This is a known control operation that issues a control command to the motor drive circuit 61 based on the target current corrected in accordance with the state and assists the steering performed as described above. During this control operation, the motor current value by the motor current sensor 60 is used as feedback information for increasing or decreasing the current for driving the steering assisting motor 6.

  The fail processing unit 50 is provided with a detection value of the vehicle speed by the vehicle speed sensor 7 and a motor current value of the motor 6 by the motor current sensor 60.

  The fail processing unit 50 includes a CPU, a ROM, and a RAM, and performs a fail determination by an operation of the CPU according to a control program stored in the ROM. This fail determination operation is an operation for determining whether or not the motor current value by the motor current sensor 60 exists in a predetermined region (fail determination region). The fail processing unit 50 outputs a stop command to the motor drive circuit 61 when it is determined that the motor current value by the motor current sensor 60 does not exist in the fail determination area.

FIG. 2 is a functional block diagram showing functions executed by the fail processing unit 50. As shown in FIG. The fail processing unit 50 includes a fail determination area setting unit 51 and a determination unit 52. The detected value of the vehicle speed by the vehicle speed sensor 7 given to the fail processing unit 50 is given to the fail determination area setting unit 51, and the fail determination area setting unit 51 fails based on the detected value of the vehicle speed by the vehicle speed sensor 7. Set the judgment area.
Further, the motor current value by the motor current sensor 60 given to the fail processing unit 50 and information indicating the fail judgment area set by the fail judgment area setting unit 51 are given to the judgment unit 52. 52 determines whether or not the motor current value by the motor current sensor 60 is in the fail determination area set by the fail determination area setting unit 51, and issues a stop command to the motor drive circuit 61 if it does not exist.

  FIG. 3 is a graph showing a control map stored in the ROM of the control unit 40 and a fail determination area set by the fail determination area setting unit 51. In the figure, the horizontal axis indicates the torque input when the steering wheel 30 is rotated, that is, the steering torque T [Nm] applied to the steering shaft 4, and the vertical axis indicates the target current I [A]. .

  A hatched area in the figure indicates a reference failure determination area A0. Further, the fail determination area A0 is an expanded area, the fail determination area corresponding to the vehicle speed V1 is A1, the fail determination area A1 is expanded, the fail determination area corresponding to the vehicle speed V2 is A2, and the fail determination area. A region in which A2 is enlarged, and a fail determination region corresponding to the vehicle speed V3 is A3 (V1> V2> V3).

  The fail determination area setting unit 51 determines a fail determination area based on a pre-stored function in which the fail determination area is continuously widened according to the slowness of the vehicle speed, for example, a function in which the fail determination area is linearly widened. A1 to A3 are set.

  Further, f1 to f3 in the figure exemplify a control map showing the relationship between the steering torque and the temporary target current. The control map corresponding to the vehicle speed V1 is f1, the control map corresponding to the vehicle speed V2 is f2, and the vehicle speed V3. The corresponding control map is f3.

  Each control map f1 to f3 is a function in which the temporary target current increases as the steering torque increases, and the magnitude of the temporary target current obtained when a predetermined steering torque is applied to each control map f1 to f3 is The temporary target current obtained from the control map f3 is the largest, followed by the temporary target current obtained from the control map f2 and the temporary target current obtained from the control map f1. In other words, the temporary target current with respect to the steering torque is set to increase as the vehicle speed decreases and is set to decrease as the vehicle speed increases. The temporary target current obtained from the control maps f1 to f3 exists in the fail determination area A0.

  Next, the relationship between the fail determination area and the target current will be described. FIG. 4 is a graph in which a part of FIG. 3 is enlarged to show the relationship between the fail determination area, the control map, and the target current.

The control unit 40 corrects the temporary target current obtained from the control map according to the steering state such as the steering angle and the steering speed, and obtains the target current. In the drawing, Fa1 (Ts) is illustrated as a target current when the steering torque is Ts and the vehicle speed is V1, and Fa2 is illustrated as the target current when the steering torque is Ts and the vehicle speed is V2. (Ts) is illustrated, and Fa3 (Ts) is illustrated as a target current when the steering torque is Ts and the vehicle speed is V3. The target current Fa1 (Ts), the target current Fa2 (Ts), and the target current Fa3 (Ts) exist in the fail determination area A1, the fail determination area A2, and the fail determination area A3, respectively.
By correcting the temporary target current, the target current Fa1 (Ts) is obtained when the steering torque is Ts and the vehicle speed is V1, and when the steering torque is Ts and the vehicle speed is V2, the target current Fa2 ( When the target current Fa3 (Ts) is obtained when the steering torque is Ts and the vehicle speed is V3, the fail processing unit 50 issues a stop command to the motor drive circuit 61 due to the correction. It will not be emitted.

  FIG. 5 is a flowchart illustrating a fail determination procedure executed by the CPU of the fail processing unit 50. The CPU of the fail processing unit 50 takes in the vehicle speed detection value of the vehicle speed sensor 7 input at an appropriate sampling cycle (step S1). Next, the CPU of the fail processing unit 50 sets a fail determination area based on the captured vehicle speed detection value (step S2). For example, when the vehicle speed is V1, the fail determination area A1 is set. When the vehicle speed is V2, the fail determination area A2 is set. When the vehicle speed is V3, the fail determination area A3 is set. Set. Then, the CPU of the fail processing unit 50 takes in the motor current value from the motor current sensor 60 (step S3).

  Then, the CPU of the fail processing unit 50 determines whether or not a motor current value exists in the set fail determination area (step S4). If the motor current value exists in the set fail determination area (step S4: YES), the fail determination is terminated. When the motor current value does not exist in the set fail determination area (step S4: NO), the CPU of the fail processing unit 50 issues a stop command to the motor drive circuit 61 (step S5), and ends the fail determination.

  When the motor current value exists in the set failure determination area, the control unit 40 is operating normally. On the other hand, when the motor current value does not exist in the set failure determination area, an abnormality has occurred in the control unit 40. In this case, a stop command is output from the fail processing unit 50 to the motor drive circuit 61, and the drive of the motor 6 is stopped.

  In FIG. 2, step S <b> 1 and step S <b> 2 are executed by the fail determination area setting unit 51, and steps S <b> 3 to S <b> 5 are executed by the determination unit 52.

  In the electric power steering apparatus according to the first embodiment, by changing the fail determination area for abnormality determination, the motor current value by the motor current sensor 60 deviates from the fail determination area, and the control unit 40 erroneously operates. It is possible to avoid the possibility that the abnormality is determined, and to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to the correction. In addition, by changing the fail judgment area according to the slow speed of the vehicle, the fail judgment area is expanded during low speed running, and the steering feeling suddenly deteriorates during low speed running where a large steering assist force is required. Can be prevented.

  In the electric power steering apparatus according to the first embodiment, when the motor 6 is driven based on the target current that is erroneously obtained by the abnormal operation of the control unit 40, the steering wheel 30 has an abnormal behavior. However, when the vehicle is traveling at high speed, the fail judgment area is reduced. Therefore, even if the difference between the target current and the temporary target current is not large, if the target current is outside the fail judgment area, the motor 6 The drive is stopped. For this reason, priority can be given to avoiding the abnormal behavior of the steering wheel 30 when traveling at high speed.

  In the electric power steering apparatus according to the first embodiment, the vehicle speed can be adjusted by setting the fail determination area based on a function that the range of the fail determination area is continuously widened according to the slowness of the vehicle speed. A corresponding fail determination area is set, and the fail processing unit 50 can make an appropriate determination according to the vehicle speed.

  In the electric power steering apparatus according to the first embodiment, the temporary target current determined based on the steering torque is corrected according to the steering state of the vehicle, and the target current is obtained, thereby steering the vehicle. It is possible to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to the change in the state.

  Further, in the electric power steering apparatus according to the first embodiment, when the controller 40 determines that the controller 40 is abnormal in the fail processing unit 50, the abnormality of the controller 40 is stopped by stopping the driving of the motor 6. It is possible to prevent the motor 6 from being driven on the basis of the target current that is erroneously obtained by a simple operation.

  In the electric power steering apparatus according to the first embodiment, it is possible to prevent the steering assist force from being lost and the steering feeling from being deteriorated due to a change in the steering angle or the steering speed.

  Even when an abnormality occurs in the motor drive circuit 61 or the motor 6, the failure processing unit 50 can determine the abnormality based on the motor current value obtained by the motor current sensor 60. Moreover, it replaces with the motor current value by the motor current sensor 60, the target current calculated | required in the control part 40 is input into the fail process part 50, and the target current calculated | required in the control part 40 exists in a failure determination area | region. May be determined by the fail determination unit 52. Further, a plurality of fail determination areas corresponding to the vehicle speed may be stored in advance, and the fail determination area setting unit 51 may select the stored fail determination area according to the slow speed of the vehicle speed.

  Since the control unit 40 issues a control command to the motor drive circuit 61 based on the target current obtained by the control unit 40, the motor current value obtained by the motor current sensor 60 is the target current obtained by the control unit 40. It corresponds to.

(Embodiment 2)
Hereinafter, the present invention will be described in detail with reference to the drawings showing an electric power steering apparatus according to a second embodiment. FIG. 6 is a functional block diagram showing functions executed by the control unit 40.
In the first embodiment, the fail processing unit 50 performs a fail determination operation. On the other hand, in the second embodiment, the control unit 40 itself performs the appropriateness determination operation. This appropriateness determination operation is an operation for determining whether or not the target current exists in a predetermined region (appropriate determination region). When it is determined that the target current does not exist in the appropriate determination range, the control unit 40 outputs a signal indicating the boundary value of the appropriate determination range to the motor drive circuit 61.

  The control unit 40 includes an appropriate determination area setting unit 41, a target current setting unit 42, and an appropriate determination unit 43. The detected value of the vehicle speed by the vehicle speed sensor 7 given to the control unit 40 is given to the appropriate determination area setting unit 41, and the appropriate determination area setting unit 41 determines the appropriateness based on the detected value of the vehicle speed by the vehicle speed sensor 7. Set the area.

  The detected value of the steering torque by the torque detection device 5 given to the control unit 40 is given to the target current setting unit 42, and the target current setting unit 42 can select a plurality of values according to the vehicle speed from the detected value of the steering torque. A temporary target current is obtained according to a stored control map, and a target current obtained by correcting the temporary target current according to a steering state such as a steering angle and a steering speed is set. Information indicating the appropriate determination area set by the appropriate determination area setting unit 41 and the target current set by the target current setting unit 42 are given to the appropriate determination unit 43. It is determined whether or not the target current set by the target current setting unit 42 is in the proper determination range set by the proper determination region setting unit 41. If not, the appropriate value corresponding to the detected value of the steering torque is determined. A boundary value drive command for driving the motor 6 at the boundary value of the determination area is issued to the motor drive circuit 61.

  FIG. 7 is a graph showing the control map stored in the ROM of the control unit 40 and the appropriate determination area set by the appropriate determination area setting unit 41.

  A hatched area in the figure represents a reference appropriateness determination area B0. In addition, the appropriate determination area B0 is an expanded area, the appropriate determination area corresponding to the vehicle speed V1 is B1, the appropriate determination area B1 is expanded, and the appropriate determination area corresponding to the vehicle speed V2 is B2, the appropriate determination area An appropriate determination area corresponding to the vehicle speed V3, which is an enlarged area of B2, is B3.

  The appropriate determination area setting unit 41 is based on a pre-stored function in which the appropriate determination area is continuously widened according to the slowness of the vehicle speed, for example, a function in which the appropriate determination area is linearly widened. B1 to B3 are set.

  Further, f1 to f3 in the figure exemplify a control map showing the relationship between the steering torque and the temporary target current. The control map corresponding to the vehicle speed V1 is f1, the control map corresponding to the vehicle speed V2 is f2, and the vehicle speed V3. The corresponding control map is f3. The temporary target current obtained from the control maps f1 to f3 exists in the appropriate determination area B0.

  Next, the relationship between the appropriate determination area and the target current will be described. FIG. 8 is a graph in which a part of FIG. 7 is enlarged to show the relationship between the appropriate determination area, the control map, and the target current.

The control unit 40 corrects the temporary target current obtained from the control map according to the steering state such as the steering angle and the steering speed, and obtains the target current. In the drawing, Fb1 (Ts) is illustrated as a target current when the steering torque is Ts and the vehicle speed is V1, and Fb2 is used as the target current when the steering torque is Ts and the vehicle speed is V2. (Ts) is illustrated, and Fb3 (Ts) is illustrated as a target current when the steering torque is Ts and the vehicle speed is V3. When the steering torque is Ts, the upper limit value of the appropriate determination area B1 is G1 (Ts), when the steering torque is Ts, the upper limit value of the appropriate determination area B2 is G2 (Ts), and the steering torque is Ts. The upper limit value of the appropriate determination area B3 is G3 (Ts). The target current Fb1 (Ts), the target current Fb2 (Ts), and the target current Fb3 (Ts) exist in the appropriate determination area B1, the appropriate determination area B2, and the appropriate determination area B3, respectively.
By correcting the temporary target current, the target current Fb1 (Ts) is obtained when the steering torque is Ts and the vehicle speed is V1, and when the steering torque is Ts and the vehicle speed is V2, the target current Fb2 ( When the target current Fb3 (Ts) is obtained when the steering torque is Ts and the vehicle speed is V3, the control unit 40 does not issue a boundary value drive command to the motor drive circuit 61.
On the other hand, when the control unit 40 obtains a target current that exceeds the appropriate determination range B1 when the steering torque is Ts and the vehicle speed is V1, for example, the upper limit value G1 (Ts ) Is output to the motor drive circuit 61. When the steering torque is Ts and the vehicle speed is V2, the target current exceeding the appropriate determination range B2 is obtained. When a signal indicating the upper limit value G2 (Ts) is output to the motor drive circuit 61 and the steering torque is Ts and the vehicle speed is V3, the target current exceeding the appropriate determination range B3 is obtained. Then, a signal indicating the upper limit value G3 (Ts) as the boundary value drive command is output to the motor drive circuit 61.

  FIG. 9 is a flowchart showing a procedure of appropriateness determination executed by the CPU of the control unit 40. The CPU of the control unit 40 takes in the vehicle speed detection value of the vehicle speed sensor 7 input at an appropriate sampling cycle (step S11). Next, the CPU of the control unit 40 sets an appropriate determination area based on the captured vehicle speed detection value (step S12). For example, when the vehicle speed is V1, the appropriate determination area B1 is set. When the vehicle speed is V2, the appropriate determination area B2 is set. When the vehicle speed is V3, the appropriate determination area B3 is set. Set. Then, the CPU of the control unit 40 sets a target current (step S13).

  The CPU of the control unit 40 determines whether or not the target current exists in the set appropriate determination range (step S14). When the target current exists in the set appropriate determination range (step S14: YES), a command for driving the motor with the target current is issued to the motor drive circuit 61 (step S15). If the target current does not exist in the set appropriate determination range (step S14: NO), the CPU of the control unit 40 issues a boundary value drive command to the motor drive circuit 61 (step S16).

  When the target current exists in the set appropriate determination range, the control unit 40 obtains an appropriate target current. In this case, a command for driving the motor with the target current is output from the control unit 40 to the motor drive circuit 61, and the motor 6 is driven with the target current. On the other hand, when the target current does not exist in the set appropriate determination range, the target current obtained by the control unit 40 may be incorrect. In this case, a boundary value drive command is output from the control unit 40 to the motor drive circuit 61, and the motor 6 is driven at the boundary value in the appropriate determination range corresponding to the detected value of the steering torque.

  In FIG. 6, steps S <b> 11 and S <b> 12 are executed by the appropriate determination area setting unit 41, step S <b> 13 is executed by the target current setting unit 42, and steps S <b> 14 to S <b> 16 are executed by the appropriate determination unit 43. Is done.

  In the electric power steering apparatus according to the second embodiment, when the target current obtained by correcting the temporary target current determined based on the steering torque according to the steering state of the vehicle is out of the appropriate determination range, the control unit 40 Issues a boundary value drive command for driving the motor 6 at the boundary value of the appropriate determination range to the motor drive circuit 61. For this reason, when the target current calculated by the control unit 40 is incorrect, the motor 6 is driven with the incorrect target current, and deterioration of the steering feeling can be prevented.

  In the electric power steering apparatus according to the second embodiment, by setting the appropriate determination area based on a function that the range of the appropriate determination area continuously widens according to the slowness of the vehicle speed, An appropriate determination area according to the vehicle speed is set, and the control unit 40 can make an appropriate determination according to the vehicle speed.

  In the electric power steering apparatus according to the second embodiment, since the appropriate determination area is made larger or smaller according to the slow speed of the vehicle speed, the appropriate determination area is enlarged and a large steering assist force is required when traveling at a low speed. This can prevent the steering feeling from abruptly deteriorating during low-speed traveling. On the other hand, since the appropriate judgment area is reduced during high-speed driving, even if the difference between the target current and the temporary target current is not large, if the target current is outside the appropriate judgment area, the boundary value of the appropriate judgment area The motor 6 is driven. For this reason, priority can be given to keeping the vehicle posture during high-speed traveling.

1 is a schematic diagram showing a configuration of an electric power steering device according to Embodiment 1. FIG. 3 is a functional block diagram illustrating functions executed by a fail processing unit according to Embodiment 1. FIG. 6 is a graph showing a failure determination area set in a control map and a failure determination area setting unit stored in the ROM of the control unit in the first embodiment. FIG. 4 is a graph in which a part of FIG. 3 is enlarged to show a relationship between a fail determination area, a control map, and a target current. 3 is a flowchart illustrating a fail determination procedure executed by a CPU of a fail processing unit according to the first embodiment. 10 is a functional block diagram illustrating functions executed by a control unit according to Embodiment 2. FIG. 10 is a graph showing a control map stored in the ROM of the control unit in Embodiment 2 and an appropriate determination area set by an appropriate determination area setting unit. It is the graph which expanded the part of FIG. 7, and showed the relationship of the appropriate determination area, the control map, and the target current. 10 is a flowchart illustrating a procedure of appropriateness determination performed by a CPU of a control unit in the second embodiment.

Explanation of symbols

  4 Steering shaft, 5 Torque detection device, 6 Motor, 7 Vehicle speed sensor, 30 Steering wheel (steering member), 40 Control unit, 41 Appropriate determination area setting unit, 42 Target current setting unit, 43 Appropriate determination unit, 50 Fail processing unit , 51 Fail determination area setting section, 52 Fail determination section, 60 Motor current sensor, 61 Motor drive circuit

Claims (5)

A motor for assisting steering, a control means for controlling driving of the motor based on a target current determined according to a steering state of the vehicle, and the control means is abnormal when the target current is not within a predetermined range. In an electric power steering device comprising a determination means for determining that
An electric power steering apparatus comprising: setting means for setting the range so that the range becomes wider and narrower according to the slow speed of the vehicle traveling speed.   2. The electric motor according to claim 1, wherein the setting means sets the range based on a function that continuously widens and narrows the range according to a slow speed of the vehicle. Power steering device.   The control means determines a target current by correcting a temporary target current determined based on a steering torque applied to a steering member according to a steering state of a vehicle. The electric power steering apparatus according to 1 or 2.   The electric power steering apparatus according to any one of claims 1 to 3, further comprising means for stopping the driving of the motor when the determination means determines that the control means is abnormal. .   The electric power steering apparatus according to any one of claims 1 to 4, wherein the steering state includes a steering angle or a steering speed.

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